1. Field of the Invention
This invention relates to methods of terminating water flow in subterranean formations during drilling operations and, more particularly, to methods of using an environmentally friendly composition comprising a hydraulic cement, a viscosifying agent and a vegetable oil for shutting off water flow in fresh water zones, water aquifers and the like.
2. Description of the Prior Art
In the operation of wells used in the recovery of fluids from or the introduction of fluids into subterranean formations problems relating to the unwanted passage of water from undesirable locations in the formation or well bore sometimes occur. This unwanted passage of water can severely disrupt or in fact terminate the desired operation of a well.
To be more specific, the problems ordinarily involve the movement of water through very small undesirable openings. These problems are not unique and the solutions have traditionally involved apparatus, methods and compositions adapted to cover, seal or to otherwise plug the openings to thereby terminate the unwanted passage of fluid therethrough. The openings referred to above include: holes or cracks in well casing; spaces such as holes, cracks, voids or channels in the cement sheath deposited in the annular space between the formation face and well casing; very small spaces called microannuli between the cement sheath, referred to above, and the exterior surface of the well casing or formation; and permeable spaces in gravel packs and formations.
Conventional substances used in sealing or plugging the holes or cracks have included diesel oil cements which are comprised of an API Class cement, a surface-active agent and diesel oil or kerosene. These diesel oil type cements do not set until they are placed in a water-bearing zone where they absorb water and set. Furthermore, the use of a substance containing diesel oil or kerosene is not always environmentally desirable for use in terminating water flow in a fresh water zone or water aquifer.
During the construction of a well it is known to place a volume of a slurry of hydraulic cement into the annular space between the walls of the borehole and the exterior of the casing wherein the cement, is permitted to solidify to thereby form an annular sheath of hardened cement. The objective of the sheath, the construction of which is referred to as primary cementing, includes physical support and positioning of the casing in the borehole and prevention of unwanted fluid (liquid and gas) migration between various formations penetrated by the well bore. If, for some reason, the hardened sheath contains spaces such as voids, cracks or channels due to problems involved in the placement of the slurry it is clear that the sheath may not be capable of providing the desired objectives. Accordingly, by employing known techniques to locate the voids, channels or cracks, a perforation penetrating the spaces can be made in the casing and sheath and a cementitious material then squeezed into the spaces via the perforation so as to place the sheath in a more desirable condition for protecting and supporting the casing and providing fluid flow control.
Another problem incidental to the formation of the cement sheath, referred to above, revolves about the occasional failure of the sheath to tightly bond to the exterior wall of the casing or the interior of the borehole. This failure can produce a very thin annular space called a microannulus between the exterior wall of the casing and the sheath or the sheath and the borehole. For the reasons already discussed, it is important to place a substance, such as a hydraulic cementitious material, in the microannulus to enable the sheath to fully provide the intended benefits.
Still another problem involved in the operation of wells which are the subject of this invention, revolves about the unwanted movement of water via cracks and fractures in the subterranean formation--whether naturally occurring or deliberately produced--from the formation into the well bore. Terminating this water movement may require remedial efforts other than those referred to previously which feature plugging perforations, holes, cracks and the like in casing, cement sheath and gravel packs--all of which occur within the confines of the well borehole itself. However, with use of the methods and compositions of this invention the unwanted movement of water from cracks and fractures in the formation outside of the well borehole itself may be prevented.
The problems referred to above explain how the unwanted passage of fluids, such as water, can occur in a well. Solutions to these and similar problems, according to this invention, involve the methods of using an environmentally friendly composition comprising hydraulic cement, a viscosifying agent and vegetable oil.